Abstract / Synopsis

Basal stem rot (BSR) is a major threat to the oil palm industry. The disease is caused by
Ganoderma boninense, which rots the internal tissues at the trunk base resulting in stem
fracture and death of palm. The present study investigated the efficacy of two isolates of
Trichoderma harzianum (BIO T32 and BIO T66) as potential biological control agents
against BSR based on in vitro and in vivo trials.
The study revealed that treatment applied as a soil drench using conidial suspension
(mean of 1.61 x lo8 sporeslml) of BIO T32 in addition to a Trichoderma-incorporated
palm press fibre (ppf) surface mulch, performed better with a significant difference
compared to the use of BIO T66. The disease severity index (DSI) of the former was
28.35 compared to 76.67 of the latter. BIO T32 was also a competent biological control
agent in the delayed treatment given to pre-infected seedlings at 6 weeks before treatment
with BIO T32, giving a DSI of 45, which was statistically significant compared to the
infected and untreated control seedlings with a DSI of 86.67. In testing the synergistic
effect by combining the 2 isolates, a poorer performance was observed based on the DSI
and plant biomass compared to single application of BIO T32. Isolate BIO T66 which
showed good antagonistic properties in the in vitro assessment was not found to display
similar results in the in vivo trials.
A series of treatments were evaluated for their potential as a BIO T32 carrier. Out of the
3 studies, only ppf and compost exhibited promising results in their capacity as surface
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mulches, where treatments with either one gave a DSI of 30. Both are food base carriers
for they increased the growth of oil palm seedlings significantly, with compost displaying
better results. Treatment with compost in terms of vegetative growth gave the highest
plant biomass, leaf area measurement, nitrogen, phosphorus and potassium (NPK)
content in the seedlings compared to the other 2 treatments of ppf and the untreated
control seedlings.
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In total, the experiment revealed that the application of BIO T32 as a single inoculum
was the best treatment, giving a DSI of 28.35. Trials using a single application of BIO
T66 and BIO T66 mixed with BIO T32 performed poorly, giving a DSI of 76.67 each and
were not significantly different from the infected non-treated control plants. An
appropriate interval of conidial suspension's application played a pertinent role in the
inhibition of disease as demonstrated in the delayed treatment. The application of
compost was found to be an interesting alternative to ppf as surface mulch, which
functions also as a Trichoderma carrier. Finally, in terms of vegetative growth both ppf
and compost as food base carriers significantly increased plant biomass, total leaf area
measurement and N uptake compared to the untreated control.